The subject invention relates to a method for rapidly determining the mass of a mail piece.
Mailing systems where a mail piece is transported onto a postal scale, the appropriate postage is determined and used to set a postage meter, and the mail piece is then transported to the postage meter for imprinting with a postal indicia representative of the postage amount are known. One such system is described in U.S. Pat. No. 4,742,878, issued May 10, 1988 to the assignee of the subject invention. In such systems, there is a constant need to increase the rate at which the scale can determine the mass of a mail piece in order that the throughput of the system can be increased. Heretofore, weighing devices for such mail processing systems have been developed, but these generally have been rather slow. Actually, many prior weight devices combined a standard scale with a mechanism that would stop the mail to allow weighing to take place. These systems require large transports and high acceleration and deceleration rates. To keep pace with a high throughout rate, multiple scales would be used with alternate mail pieces diverted to such scales.
A separate approach for providing high throughput mailing systems has been the use of vibrating tray scales to determine the mass of a mail piece where the mass is estimated as a function of the frequency at which a scale tray vibrates after a mail piece is placed upon it and the system is excited. Such a system is described in U.S. Pat. No. 5,082,072. While such prior art systems have proven generally satisfactory, there is still a need for a method of operation which is suitable for use with load cell technology while still providing desired high throughput rates of at least three mail pieces per second for mailing systems.